1. Field of the Invention
The present invention relates generally to shipboard electrical systems, and more particularly to apparatus and methods for converting electrical alternating current (AC) shore power for shipboard use.
2. Description of the Related Art
Most modern military and commercial ships have a plethora of electrical equipment requiring alternating current (AC) power for operation. The AC power is generally supplied via at least one main power distribution bus which is electrically connected to one or more sources of AC power. When a ship is at sea, the source of AC power is a shipboard service generator that is coupled to a prime mover, such as a diesel engine, a steam or gas turbine, or even a large direct current battery (through a motor-generator DC-AC converter).
It happens that a shipboard service generator typically outputs AC power having substantially fixed voltage, frequency, and phase characteristics. Consequently, the ship's AC power distribution system is designed with a particular main distribution bus voltage, frequency, and phase in mind. In other words, to properly operate the various electrical components of a ship, AC power having predetermined voltage, frequency, and phase characteristics must be provided.
While AC power is supplied at sea by the ship's service generator, in port it is desirable to connect the main distribution bus to a dockside source of AC shore power to permit electrically disconnecting the service generator from the bus and then deactivating the service generator. In this way, prime mover fuel is conserved and maintenance on the service generator system can be performed, without interrupting power to various shipboard electrical components.
Unfortunately, it happens that before connecting the ship's main distribution to AC shore power, the ship's main distribution must be disconnected from the ship's generator AC output causing a power interruption to the shipboard electrical components. Furthermore, it happens that the electrical characteristics of shore power sources can vary widely from port to port and for this reason, it is sometimes necessary to convert power having first characteristics of voltage, frequency and phase, to ship service power having second characteristics of voltage, frequency and phase, to permit energizing shipboard electrical components with the shore power.
As recognized by the present invention, however, standard electrical power transformation devices can be limited in the input electrical characteristics they are able to convert. Stated differently, a standard transformer device may be capable of converting shore power only in some ports to shipboard use, but not be sufficiently operationally flexible to convert shore power voltage, frequency and phase in other ports to shipboard use, because of potentially widely varying shore power characteristics from port to port. Consequently, in ports that supply shore power with voltage, frequency and phase characteristics that are outside the capability of a ship's transformer device to convert, it is necessary for the ship to continue to operate its service generator to power shipboard electrical components during its entire stay in port.
Accordingly, the present invention recognizes that it would be advantageous to provide a power converter which can convert shore power to shipboard use and also transfer the ship's main power distribution bus to the AC shore power without interrupting power to various shipboard electrical components. It is, therefore, an object of the present invention to provide a power converter for converting shore power to shipboard use and to transfer the ship's load from one power path to another without interrupting power to various shipboard electrical components and which can be used in most ports around the world. Another objective of the present invention is to provide a power converter for converting shore power to shipboard use which can convert input power having first characteristics of voltage, frequency and phase, to output power having second characteristics of voltage, frequency and phase. A further objective of the present invention is to provide a power converter for transferring the shipboard electrical components from one shipboard generator to second or third shipboard generator without interrupting power to various shipboard electrical components. Still another object o the present invention is to provide a power converter for converting shore power to shipboard use which is easy to use and cost effective.